haspositionalpredchecker.java

来自「java jdk 1.4的源码」· Java 代码 · 共 105 行

package org.apache.xpath.axes;

import org.apache.xpath.Expression;
import org.apache.xpath.ExpressionOwner;
import org.apache.xpath.XPathVisitor;
import org.apache.xpath.functions.FuncLast;
import org.apache.xpath.functions.FuncPosition;
import org.apache.xpath.functions.Function;
import org.apache.xpath.objects.XNumber;
import org.apache.xpath.operations.Div;
import org.apache.xpath.operations.Minus;
import org.apache.xpath.operations.Mod;
import org.apache.xpath.operations.Mult;
import org.apache.xpath.operations.Plus;
import org.apache.xpath.operations.Quo;
import org.apache.xpath.operations.Variable;

public class HasPositionalPredChecker extends XPathVisitor
{
	private boolean m_hasPositionalPred = false;
	private int m_predDepth = 0;
	
	/**
	 * Process the LocPathIterator to see if it contains variables 
	 * or functions that may make it context dependent.
	 * @param path LocPathIterator that is assumed to be absolute, but needs checking.
	 * @return true if the path is confirmed to be absolute, false if it 
	 * may contain context dependencies.
	 */
	public static boolean check(LocPathIterator path)
	{
		HasPositionalPredChecker hppc = new HasPositionalPredChecker();
		path.callVisitors(null, hppc);
		return hppc.m_hasPositionalPred;
	}
	
	/**
	 * Visit a function.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param func The function reference object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitFunction(ExpressionOwner owner, Function func)
	{
		if((func instanceof FuncPosition) ||
		   (func instanceof FuncLast))
			m_hasPositionalPred = true;
		return true;
	}
	
//	/**
//	 * Visit a variable reference.
//	 * @param owner The owner of the expression, to which the expression can 
//	 *              be reset if rewriting takes place.
//	 * @param var The variable reference object.
//	 * @return true if the sub expressions should be traversed.
//	 */
//	public boolean visitVariableRef(ExpressionOwner owner, Variable var)
//	{
//		m_hasPositionalPred = true;
//		return true;
//	}
	
  /**
   * Visit a predicate within a location path.  Note that there isn't a 
   * proper unique component for predicates, and that the expression will 
   * be called also for whatever type Expression is.
   * 
   * @param owner The owner of the expression, to which the expression can 
   *              be reset if rewriting takes place.
   * @param pred The predicate object.
   * @return true if the sub expressions should be traversed.
   */
  public boolean visitPredicate(ExpressionOwner owner, Expression pred)
  {
    m_predDepth++;

    if(m_predDepth == 1)
    {
      if((pred instanceof Variable) || 
         (pred instanceof XNumber) ||
         (pred instanceof Div) ||
         (pred instanceof Plus) ||
         (pred instanceof Minus) ||
         (pred instanceof Mod) ||
         (pred instanceof Quo) ||
         (pred instanceof Mult) ||
         (pred instanceof org.apache.xpath.operations.Number) ||
         (pred instanceof Function))
          m_hasPositionalPred = true;
      else
      	pred.callVisitors(owner, this);
    }

    m_predDepth--;

    // Don't go have the caller go any further down the subtree.
    return false;
  }


}